Data distribution fabric in scalable GPUs

ABSTRACT

In on embodiment, a hybrid fabric interconnects multiple graphics processor cores within a processor. The hybrid fabric interconnect includes multiple data channels, including programmable virtual data channels. The virtual data channels carry multiple traffic classes of packet-based messages. The virtual data channels and multiple traffic classes may be assigned one of multiple priorities. The virtual data channels may be arbitrated independently. The hybrid fabric is scalable and can support multiple topologies, including multiple stacked integrated circuit topologies.

BACKGROUND

1. Field of the Disclosure

Embodiments are generally related to information processing, and moreparticularly to a data distribution fabric for use in scalable graphicsprocessors.

2. Description of the Related Art

Multi-core graphics processing units have become normalized amongcomputing systems ranging from system on a chip (SOC) integratedcircuits to high-end discrete graphics processors. In the real ofhigh-end graphics, multi-core solutions are the primary method ofincreasing graphics processing performance. For SOC solutions, the useof multi-core graphics processors allows a reduction in system powerwhile allowing high performance during periods of high graphicsprocessor workload.

However, the increase in the number of graphics cores within a componentcreates scalability issues when developing graphics processing solutionsthat span multiple power and performance segments. The multi-corecommunication solutions used in high-end graphics products are notsuitable for low-power products due to issues of cost and powerconsumption. The communication solutions used in low-power graphicsgenerally do not provide sufficient performance for high-end graphicssolutions. For example, one graphics core communication solution is tocouple the various graphics processors via unique data distributionchannels. However, using unique communication channels presentsdifficulties for designing graphics processors that are intended to spanmultiple power and performance segments.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussion of figures havingillustrations given by way of example of implementations of the variousembodiments. The figures should be understood by way of example, and notby way of limitation, in which:

FIG. 1 is a block diagram of an embodiment of a computer system with aprocessor having one or more processor cores and graphics processors;

FIG. 2 is a block diagram of one embodiment of a processor having one ormore processor cores, an integrated memory controller, and an integratedgraphics processor;

FIG. 3 is a block diagram of one embodiment of a graphics processorwhich may be a discreet graphics processing unit, or may be graphicsprocessor integrated with a plurality of processing cores;

FIG. 4 is a block diagram of an embodiment of a graphics-processingengine for a graphics processor;

FIG. 5 is a block diagram of another embodiment of a graphics processor;

FIG. 6 is a block diagram of thread execution logic including an arrayof processing elements;

FIG. 7 illustrates a graphics processor execution unit instructionformat according to an embodiment;

FIG. 8 is a block diagram of another embodiment of a graphics processorwhich includes a graphics pipeline, a media pipeline, a display engine,thread execution logic, and a render output pipeline;

FIG. 9A is a block diagram illustrating a graphics processor commandformat according to an embodiment;

FIG. 9B is a block diagram illustrating a graphics processor commandsequence according to an embodiment;

FIG. 10 illustrates exemplary graphics software architecture for a dataprocessing system according to an embodiment;

FIG. 11 is a block diagram of an embodiment of a graphics core fabricassembly;

FIGS. 12A-B illustrate multiple exemplary graphics core topologies;

FIG. 13 is a block diagram of an embodiment of a stacked integratedcircuit including an data distribution fabric;

FIG. 14 is an illustration of multiple traffic classes carried overvirtual channels, according to an embodiment; and

FIG. 15 is a flow diagram of a data transmission sequence, according toan embodiment.

DETAILED DESCRIPTION

The following description describes processing logic for a datadistribution fabric for use in scalable graphics processing unitsincluded within or in association with a processor, computer system, orother processing apparatus. For the purposes of explanation, numerousspecific details are set forth to provide a thorough understanding ofthe various embodiments described below. However, it will be apparent toa skilled practitioner in the art that the embodiments may be practicedwithout some of these specific details. In other instances, well-knownstructures and devices are shown in block diagram form to avoidobscuring the underlying principles, and to provide a more thoroughunderstanding of embodiments.

Although some of the following embodiments are described with referenceto a processor, similar techniques and teachings can be applied to othertypes of circuits or semiconductor devices, as the teachings areapplicable to any processor or machine that performs data manipulations.

Overview—FIGS. 1-3

FIG. 1 is a block diagram of a data processing system 100, according toan embodiment. The data processing system 100 includes one or moreprocessors 102 and one or more graphics processors 108, and may be asingle processor desktop system, a multiprocessor workstation system, ora server system having a large number of processors 102 or processorcores 107. In on embodiment, the data processing system 100 is a systemon a chip integrated circuit (SOC) for use in mobile, handheld, orembedded devices.

An embodiment of the data processing system 100 can include or beincorporated within a server based gaming platform or a game console,including a game and media console, a mobile gaming console, a handheldgame console, or an online game console. In one embodiment, the dataprocessing system 100 is a mobile phone, smart phone, tablet computingdevice or mobile Internet device. The data processing system 100 canalso include, couple with, or be integrated within a wearable device,such as a smart watch wearable device, smart eyewear device, augmentedreality device, or virtual reality device. In one embodiment, the dataprocessing system 100 is a television or set top box device having oneor more processors 102 and a graphical interface generated by one ormore graphics processors 108.

The one or more processors 102 each include one or more processor cores107 to process instructions which, when executed, perform operations forsystem and user software. In one embodiment, each of the one or moreprocessor cores 107 is configured to process a specific instruction set109. The instruction set 109 may facilitate complex instruction setcomputing (CISC), reduced instruction set computing (RISC), or computingvia a very long instruction word (VLIW). Multiple processor cores 107may each process a different instruction set 109 which may includeinstructions to facilitate the emulation of other instruction sets. Aprocessor core 107 may also include other processing devices, such adigital signal processor (DSP).

In one embodiment, each of the one or more processors 102 includes cachememory 104. Depending on the architecture, the processor 102 can have asingle internal cache or multiple levels of internal cache. In oneembodiment, the cache memory is shared among various components of theprocessor 102. In one embodiment, the processor 102 also uses anexternal cache (e.g., a Level 3 (L3) cache or last level cache (LLC))(not shown) which may be shared among the processor cores 107 usingknown cache coherency techniques. A register file 106 is additionallyincluded in the processor 102 which may include different types ofregisters for storing different types of data (e.g., integer registers,floating point registers, status registers, and an instruction pointerregister). Some registers may be general-purpose registers, while otherregisters may be specific to the design of the processor 102.

The processor 102 is coupled to a processor bus 110 to transmit datasignals between the processor 102 and other components in the system100. The system 100 uses an exemplary ‘hub’ system architecture,including a memory controller hub 116 and an input output (I/O)controller hub 130. The memory controller hub 116 facilitatescommunication between a memory device and other components of the system100, while the I/O controller hub (ICH) 130 provides connections to I/Odevices via a local I/O bus.

The memory device 120, can be a dynamic random access memory (DRAM)device, a static random access memory (SRAM) device, flash memorydevice, or some other memory device having suitable performance to serveas process memory. The memory 120 can store data 122 and instructions121 for use when the processor 102 executes a process. The memorycontroller hub 116 also couples with an optional external graphicsprocessor 112, which may communicate with the one or more graphicsprocessor 108 in the processor 102 to perform graphics and mediaoperations. The ICH 130 enables peripherals to connect to the memory 120and processor 102 via a high-speed I/O bus. The I/O peripherals includean audio controller 146, a firmware interface 128, a wirelesstransceiver 126 (e.g., Wi-Fi, Bluetooth), a data storage device 124(e.g., hard disk drive, flash memory, etc.), and a legacy I/O controllerfor coupling legacy (e.g., Personal System 2 (PS/2)) devices to thesystem. One or more Universal Serial Bus (USB) controllers 142 connectinput devices, such as keyboard and mouse 144 combinations. A networkcontroller 134 may also couple to the ICH 130. In one embodiment, ahigh-performance network controller (not shown) couples to the processorbus 110.

FIG. 2 is a block diagram of an embodiment of a processor 200 having oneor more processor cores 202A-N, an integrated memory controller 214, andan integrated graphics processor 208. The processor 200 can includeadditional cores up to and including additional core 202N represented bythe dashed lined boxes. Each of the cores 202A-N includes one or moreinternal cache units 204A-N. In one embodiment each core also has accessto one or more shared cached units 206.

The internal cache units 204A-N and shared cache units 206 represent acache memory hierarchy within the processor 200. The cache memoryhierarchy may include at least one level of instruction and data cachewithin each core and one or more levels of shared mid-level cache, suchas a level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache,where the highest level of cache before external memory is classified asthe last level cache (LLC). In one embodiment, cache coherency logicmaintains coherency between the various cache units 206 and 204A-N.

The processor 200 may also include a set of one or more bus controllerunits 216 and a system agent 210. The one or more bus controller unitsmanage a set of peripheral buses, such as one or more PeripheralComponent Interconnect buses (e.g., PCI, PCI Express). The system agent210 provides management functionality for the various processorcomponents. In one embodiment, the system agent 210 includes one or moreintegrated memory controllers 214 to manage access to various externalmemory devices (not shown).

In one embodiment, one or more of the cores 202A-N include support forsimultaneous multi-threading. In such embodiment, the system agent 210includes components for coordinating and operating cores 202A-N duringmulti-threaded processing. The system agent 210 may additionally includea power control unit (PCU), which includes logic and components toregulate the power state of the cores 202A-N and the graphics processor208.

The processor 200 additionally includes a graphics processor 208 toexecute graphics processing operations. In one embodiment, the graphicsprocessor 208 couples with the set of shared cache units 206, and thesystem agent unit 210, including the one or more integrated memorycontrollers 214. In one embodiment, a display controller 211 is coupledwith the graphics processor 208 to drive graphics processor output toone or more coupled displays. The display controller 211 may be separatemodule coupled with the graphics processor via at least oneinterconnect, or may be integrated within the graphics processor 208 orsystem agent 210.

In one embodiment a ring based interconnect unit 212 is used to couplethe internal components of the processor 200, however an alternativeinterconnect unit may be used, such as a point to point interconnect, aswitched interconnect, or other techniques, including techniques wellknown in the art. In one embodiment, the graphics processor 208 coupleswith the ring interconnect 212 via an I/O link 213.

The exemplary I/O link 213 represents at least one of multiple varietiesof I/O interconnects, including an on package I/O interconnect whichfacilitates communication between various processor components and ahigh-performance embedded memory module 218, such as an eDRAM module. Inone embodiment each of the cores 202-N and the graphics processor 208use the embedded memory modules 218 as shared last level cache.

In one embodiment cores 202A-N are homogenous cores executing the sameinstruction set architecture. In another embodiment, the cores 202A-Nare heterogeneous in terms of instruction set architecture (ISA), whereone or more of the cores 202A-N execute a first instruction set, whileat least one of the other cores executes a subset of the firstinstruction set or a different instruction set.

The processor 200 can be a part of or implemented on one or moresubstrates using any of a number of process technologies, for example,Complementary metal-oxide-semiconductor (CMOS), BipolarJunction/Complementary metal-oxide-semiconductor (BiCMOS) or N-typemetal-oxide-semiconductor logic (NMOS). Additionally, the processor 200can be implemented on one or more chips or as a system on a chip (SOC)integrated circuit having the illustrated components, in addition toother components.

FIG. 3 is a block diagram of one embodiment of a graphics processor 300which may be a discreet graphics processing unit, or may be graphicsprocessor integrated with a plurality of processing cores. In oneembodiment, the graphics processor is communicated with via a memorymapped I/O interface to registers on the graphics processor and viacommands placed into the processor memory. The graphics processor 300includes a memory interface 314 to access memory. The memory interface314 can be an interface to local memory, one or more internal caches,one or more shared external caches, and/or to system memory.

The graphics processor 300 also includes a display controller 302 todrive display output data to a display device 320. The displaycontroller 302 includes hardware for one or more overlay planes for thedisplay and composition of multiple layers of video or user interfaceelements. In one embodiment the graphics processor 300 includes a videocodec engine 306 to encode, decode, or transcode media to, from, orbetween one or more media encoding formats, including, but not limitedto Moving Picture Experts Group (MPEG) formats such as MPEG-2, AdvancedVideo Coding (AVC) formats such as H.264/MPEG-4 AVC, as well as theSociety of Motion Picture & Television Engineers (SMPTE) 421 M/VC-1, andJoint Photographic Experts Group (JPEG) formats such as JPEG, and MotionJPEG (MJPEG) formats.

In one embodiment, the graphics processor 300 includes a block imagetransfer (BLIT) engine 304 to perform two-dimensional (2D) rasterizeroperations including, for example, bit-boundary block transfers.However, in one embodiment, 2D graphics operations are performed usingone or more components of the graphics-processing engine (GPE) 310. Thegraphics-processing engine 310 is a compute engine for performinggraphics operations, including three-dimensional (3D) graphicsoperations and media operations.

The GPE 310 includes a 3D pipeline 312 for performing 3D operations,such as rendering three-dimensional images and scenes using processingfunctions that act upon 3D primitive shapes (e.g., rectangle, triangle,etc.). The 3D pipeline 312 includes programmable and fixed functionelements that perform various tasks within the element and/or spawnexecution threads to a 3D/Media sub-system 315. While the 3D pipeline312 can be used to perform media operations, an embodiment of the GPE310 also includes a media pipeline 316 that is specifically used toperform media operations, such as video post processing and imageenhancement.

In one embodiment, the media pipeline 316 includes fixed function orprogrammable logic units to perform one or more specialized mediaoperations, such as video decode acceleration, video de-interlacing, andvideo encode acceleration in place of, or on behalf of the video codecengine 306. In on embodiment, the media pipeline 316 additionallyincludes a thread spawning unit to spawn threads for execution on the3D/Media sub-system 315. The spawned threads perform computations forthe media operations on one or more graphics execution units included inthe 3D/Media sub-system.

The 3D/Media subsystem 315 includes logic for executing threads spawnedby the 3D pipeline 312 and media pipeline 316. In one embodiment, thepipelines send thread execution requests to the 3D/Media subsystem 315,which includes thread dispatch logic for arbitrating and dispatching thevarious requests to available thread execution resources. The executionresources include an array of graphics execution units to process the 3Dand media threads. In one embodiment, the 3D/Media subsystem 315includes one or more internal caches for thread instructions and data.In one embodiment, the subsystem also includes shared memory, includingregisters and addressable memory, to share data between threads and tostore output data.

3D/Media Processing— FIG. 4

FIG. 4 is a block diagram of an embodiment of a graphics processingengine 410 for a graphics processor. In one embodiment, the graphicsprocessing engine (GPE) 410 is a version of the GPE 310 shown in FIG. 3.The GPE 410 includes a 3D pipeline 412 and a media pipeline 416, each ofwhich can be either different from or similar to the implementations ofthe 3D pipeline 312 and the media pipeline 316 of FIG. 3.

In one embodiment, the GPE 410 couples with a command streamer 403,which provides a command stream to the GPE 3D and media pipelines 412,416. The command streamer 403 is coupled to memory, which can be systemmemory, or one or more of internal cache memory and shared cache memory.The command streamer 403 receives commands from the memory and sends thecommands to the 3D pipeline 412 and/or media pipeline 416. The 3D andmedia pipelines process the commands by performing operations via logicwithin the respective pipelines or by dispatching one or more executionthreads to the execution unit array 414. In one embodiment, theexecution unit array 414 is scalable, such that the array includes avariable number of execution units based on the target power andperformance level of the GPE 410.

A sampling engine 430 couples with memory (e.g., cache memory or systemmemory) and the execution unit array 414. In one embodiment, thesampling engine 430 provides a memory access mechanism for the scalableexecution unit array 414 that allows the execution array 414 to readgraphics and media data from memory. In one embodiment, the samplingengine 430 includes logic to perform specialized image samplingoperations for media.

The specialized media sampling logic in the sampling engine 430 includesa de-noise/de-interlace module 432, a motion estimation module 434, andan image scaling and filtering module 436. The de-noise/de-interlacemodule 432 includes logic to perform one or more of a de-noise or ade-interlace algorithm on decoded video data. The de-interlace logiccombines alternating fields of interlaced video content into a singlefame of video. The de-noise logic reduces or remove data noise fromvideo and image data. In one embodiment, the de-noise logic andde-interlace logic are motion adaptive and use spatial or temporalfiltering based on the amount of motion detected in the video data. Inone embodiment, the de-noise/de-interlace module 432 includes dedicatedmotion detection logic (e.g., within the motion estimation engine 434).

The motion estimation engine 434 provides hardware acceleration forvideo operations by performing video acceleration functions such asmotion vector estimation and prediction on video data. The motionestimation engine determines motion vectors that describe thetransformation of image data between successive video frames. In oneembodiment, a graphics processor media codec uses the video motionestimation engine 434 to perform operations on video at the macro-blocklevel that may otherwise be computationally intensive to perform using ageneral-purpose processor. In one embodiment, the motion estimationengine 434 is generally available to graphics processor components toassist with video decode and processing functions that are sensitive oradaptive to the direction or magnitude of the motion within video data.

The image scaling and filtering module 436 performs image-processingoperations to enhance the visual quality of generated images and video.In one embodiment, the scaling and filtering module 436 processes imageand video data during the sampling operation before providing the datato the execution unit array 414.

In one embodiment, the graphics processing engine 410 includes a dataport 444, which provides an additional mechanism for graphics subsystemsto access memory. The data port 444 facilitates memory access foroperations including render target writes, constant buffer reads,scratch memory space reads/writes, and media surface accesses. In oneembodiment, the data port 444 includes cache memory space to cacheaccesses to memory. The cache memory can be a single data cache orseparated into multiple caches for the multiple subsystems that accessmemory via the data port (e.g., a render buffer cache, a constant buffercache, etc.). In one embodiment, threads executing on an execution unitin the execution unit array 414 communicate with the data port byexchanging messages via a data distribution interconnect that coupleseach of the sub-systems of the graphics processing engine 410.

Execution Units—FIGS. 5-7

FIG. 5 is a block diagram of another embodiment of a graphics processorhaving a scalable number of graphics cores. In one embodiment, thegraphics processor includes a ring interconnect 502, a pipelinefront-end 504, a media engine 537, and graphics cores 580A-N. The ringinterconnect 502 couples the graphics processor to other processingunits, including other graphics processors or one or moregeneral-purpose processor cores. In one embodiment, the graphicsprocessor is one of many processors integrated within a multi-coreprocessing system.

The graphics processor receives batches of commands via the ringinterconnect 502. The incoming commands are interpreted by a commandstreamer 503 in the pipeline front-end 504. The graphics processorincludes scalable execution logic to perform 3D geometry processing andmedia processing via the graphics core(s) 580A-N. For 3D geometryprocessing commands, the command streamer 503 supplies the commands tothe geometry pipeline 536. For at least some media processing commands,the command streamer 503 supplies the commands to a video front end 534,which couples with a media engine 537. The media engine 537 includes avideo quality engine (VQE) 530 for video and image post processing and amulti-format encode/decode (MFX) 533 engine to providehardware-accelerated media data encode and decode. The geometry pipeline536 and media engine 537 each generate execution threads for the threadexecution resources provided by at least one graphics core 580A.

The graphics processor includes scalable thread execution resourcesfeaturing modular cores 580A-N (sometime referred to as core slices),each having multiple sub-cores 550A-N, 560A-N (sometimes referred to ascore sub-slices). The graphics processor can have any number of graphicscores 580A through 580N. In one embodiment, the graphics processorincludes a graphics core 580A having at least a first sub-core 550A anda second core sub-core 560A. In another embodiment, the graphicsprocessor is a low power processor with a single sub-core (e.g., 550A).In one embodiment, the graphics processor includes multiple graphicscores 580A-N, each including a set of first sub-cores 550A-N and a setof second sub-cores 560A-N. Each sub-core in the set of first sub-cores550A-N includes at least a first set of execution units 552A-N andmedia/texture samplers 554A-N. Each sub-core in the set of secondsub-cores 560A-N includes at least a second set of execution units562A-N and samplers 564A-N. In one embodiment, each sub-core 550A-N,560A-N shares a set of shared resources 570A-N. In one embodiment, theshared resources include shared cache memory and pixel operation logic.Other shared resources may also be included in the various embodimentsof the graphics processor.

FIG. 6 illustrates an embodiment of thread execution logic 600 includingan array of processing elements. In one embodiment, the thread executionlogic 600 includes a pixel shader 602, a thread dispatcher 604,instruction cache 606, a scalable execution unit array including aplurality of execution units 608A-N, a sampler 610, a data cache 612,and a data port 614. In one embodiment the included components areinterconnected via an interconnect fabric that links to each of thecomponents. The thread execution logic 600 includes one or moreconnections to memory, such as system memory or cache memory, throughone or more of the instruction cache 606, the data port 614, the sampler610, and the execution unit array 608A-N. In one embodiment, eachexecution unit (e.g. 608A) is an individual vector processor capable ofexecuting multiple simultaneous threads and processing multiple dataelements in parallel for each thread. The execution unit array 608A-Nincludes any number individual execution units.

In one embodiment, the execution unit array 608A-N is primarily used toexecute “shader” programs. In one embodiment, the execution units in thearray 608A-N execute an instruction set that includes native support formany standard 3D graphics shader instructions, such that shader programsfrom graphics libraries (e.g., Direct 3D and OpenGL) are executed with aminimal translation. The execution units support vertex and geometryprocessing (e.g., vertex programs, geometry programs, vertex shaders),pixel processing (e.g., pixel shaders, fragment shaders) andgeneral-purpose processing (e.g., compute and media shaders).

Each execution unit in the execution unit array 608A-N operates onarrays of data elements. The number of data elements is the “executionsize,” or the number of channels for the instruction. An executionchannel is a logical unit of execution for data element access, masking,and flow control within instructions. The number of channels may beindependent of the number of physical ALUs or FPUs for a particulargraphics processor. The execution units 608A-N support integer andfloating-point data types.

The execution unit instruction set includes single instruction multipledata (SIMD) instructions. The various data elements can be stored as apacked data type in a register and the execution unit will process thevarious elements based on the data size of the elements. For example,when operating on a 256-bit wide vector, the 256 bits of the vector arestored in a register and the execution unit operates on the vector asfour separate 64-bit packed data elements (quad-word (QW) size dataelements), eight separate 32-bit packed data elements (double word (DW)size data elements), sixteen separate 16-bit packed data elements (word(W) size data elements), or thirty-two separate 8-bit data elements(byte (B) size data elements). However, different vector widths andregister sizes are possible.

One or more internal instruction caches (e.g., 606) are included in thethread execution logic 600 to cache thread instructions for theexecution units. In one embodiment, one or more data caches (e.g., 612)are included to cache thread data during thread execution. A sampler 610is included to provide texture sampling for 3D operations and mediasampling for media operations. In one embodiment, the sampler 610includes specialized texture or media sampling functionality to processtexture or media data during the sampling process before providing thesampled data to an execution unit.

During execution, the graphics and media pipelines send threadinitiation requests to the thread execution logic 600 via threadspawning and dispatch logic. The thread execution logic 600 includes alocal thread dispatcher 604 that arbitrates thread initiation requestsfrom the graphics and media pipelines and instantiates the requestedthreads on one or more execution units 608A-N. For example, the geometrypipeline (e.g., 536 of FIG. 5) dispatches vertex processing,tessellation, or geometry processing threads to the thread executionlogic 600. The thread dispatcher 604 can also process runtime threadspawning requests from the executing shader programs.

Once a group of geometric objects have been processed and rasterizedinto pixel data, the pixel shader 602 is invoked to further computeoutput information and cause results to be written to output surfaces(e.g., color buffers, depth buffers, stencil buffers, etc.). In oneembodiment, the pixel shader 602 calculates the values of the variousvertex attributes that are to be interpolated across the rasterizedobject. The pixel shader 602 then executes an API-supplied pixel shaderprogram. To execute the pixel shader program, the pixel shader 602dispatches threads to an execution unit (e.g., 608A) via the threaddispatcher 604. The pixel shader 602 uses texture sampling logic in thesampler 610 to access texture data in texture maps stored in memory.Arithmetic operations on the texture data and the input geometry datacompute pixel color data for each geometric fragment, or discards one ormore pixels from further processing.

In one embodiment, the data port 614 provides a memory access mechanismfor the thread execution logic 600 output processed data to memory forprocessing on a graphics processor output pipeline. In one embodiment,the data port 614 includes or couples to one or more cache memories(e.g., data cache 612) to cache data for memory access via the dataport.

FIG. 7 is a block diagram illustrating a graphics processor executionunit instruction format according to an embodiment. In one embodiment,the graphics processor execution units support an instruction set havinginstructions in multiple formats. The solid lined boxes illustrate thecomponents that are generally included in an execution unit instruction,while the dashed lines include components that are optional or that areonly included in a sub-set of the instructions. The instruction formatdescribed an illustrated are macro-instructions, in that they areinstructions supplied to the execution unit, as opposed tomicro-operations resulting from instruction decode once the instructionis processed.

In one embodiment, the graphics processor execution units nativelysupport instructions in a 128-bit format 710. A 64-bit compactedinstruction format 730 is available for some instructions based on theselected instruction, instruction options, and number of operands. Thenative 128-bit format 710 provides access to all instruction options,while some options and operations are restricted in the 64-bit format730. The native instructions available in the 64-bit format 730 variesby embodiment. In one embodiment, the instruction is compacted in partusing a set of index values in an index field 713. The execution unithardware references a set of compaction tables based on the index valuesand uses the compaction table outputs to reconstruct a nativeinstruction in the 128-bit format 710.

For each format, an instruction opcode 712 defines the operation thatthe execution unit is to perform. The execution units execute eachinstruction in parallel across the multiple data elements of eachoperand. For example, in response to an add instruction the executionunit performs a simultaneous add operation across each color channelrepresenting a texture element or picture element. By default, theexecution unit performs each instruction across all data channels of theoperands. An instruction control field 712 enables control over certainexecution options, such as channels selection (e.g., predication) anddata channel order (e.g., swizzle). For 128-bit instructions 710 anexec-size field 716 limits the number of data channels that will beexecuted in parallel. The exec-size field 716 is not available for usein the 64-bit compact instruction format 730.

Some execution unit instructions have up to three operands including twosource operands, src0 722, src1 722, and one destination 718. In oneembodiment, the execution units support dual destination instructions,where one of the destinations is implied. Data manipulation instructionscan have a third source operand (e.g., SRC2 724), where the instructionopcode JJ12 determines the number of source operands. An instruction'slast source operand can be an immediate (e.g., hard-coded) value passedwith the instruction.

In one embodiment instructions are grouped based on opcode bit-fields tosimplify Opcode decode 740. For an 8-bit opcode, bits 4, 5, and 6 allowthe execution unit to determine the type of opcode. The precise opcodegrouping shown is exemplary. In one embodiment, a move and logic opcodegroup 742 includes data movement and logic instructions (e.g., mov,cmp). The move and logic group 742 shares the five most significant bits(MSB), where move instructions are in the form of 0000xxxxb (e.g., 0x0x)and logic instructions are in the form of 0001xxxxb (e.g., 0x01). A flowcontrol instruction group 744 (e.g., call, jmp) includes instructions inthe form of 0010xxxxb (e.g., 0x20). A miscellaneous instruction group746 includes a mix of instructions, including synchronizationinstructions (e.g., wait, send) in the form of 0011xxxxb (e.g., 0x30). Aparallel math instruction group 748 includes component-wise arithmeticinstructions (e.g., add, mul) in the form of 0100xxxxb (e.g., 0x40). Theparallel math group 748 performs the arithmetic operations in parallelacross data channels. The vector math group 750 includes arithmeticinstructions (e.g., dp4) in the form of 0101xxxxb (e.g., 0x50). Thevector math group performs arithmetic such as dot product calculationson vector operands.

Graphics Pipeline—FIG. 8

FIG. 8 is a block diagram of another embodiment of a graphics processorwhich includes a graphics pipeline 820, a media pipeline 830, a displayengine 840, thread execution logic 850, and a render output pipeline870. In one embodiment, the graphics processor is a graphics processorwithin a multi-core processing system that includes one or more generalpurpose processing cores. The graphics processor is controlled byregister writes to one or more control registers (not shown) or viacommands issued to the graphics processor via a ring interconnect 802.The ring interconnect 802 couples the graphics processor to otherprocessing components, such as other graphics processors orgeneral-purpose processors. Commands from the ring interconnect areinterpreted by a command streamer 803 which supplies instructions toindividual components of the graphics pipeline 820 or media pipeline830.

The command streamer 803 directs the operation of a vertex fetcher 805component that reads vertex data from memory and executesvertex-processing commands provided by the command streamer 803. Thevertex fetcher 805 provides vertex data to a vertex shader 807, whichperforms coordinate space transformation and lighting operations to eachvertex. The vertex fetcher 805 and vertex shader 807 executevertex-processing instructions by dispatching execution threads to theexecution units 852A, 852B via a thread dispatcher 831.

In one embodiment, the execution units 852A, 852B are an array of vectorprocessors having an instruction set for performing graphics and mediaoperations. The execution units 852A, 852B have an attached L1 cache 851that is specific for each array or shared between the arrays. The cachecan be configured as a data cache, an instruction cache, or a singlecache that is partitioned to contain data and instructions in differentpartitions.

In one embodiment, the graphics pipeline 820 includes tessellationcomponents to perform hardware-accelerated tessellation of 3D objects. Aprogrammable hull shader 811 configures the tessellation operations. Aprogrammable domain shader 817 provides back-end evaluation oftessellation output. A tessellator 813 operates at the direction of thehull shader 811 and contains special purpose logic to generate a set ofdetailed geometric objects based on a coarse geometric model that isprovided as input to the graphics pipeline 820. If tessellation is notused, the tessellation components 811, 813, 817 can be bypassed.

The complete geometric objects can be processed by a geometry shader 819via one or more threads dispatched to the execution units 852A, 852B, orcan proceed directly to the clipper 829. The geometry shader operates onentire geometric objects, rather than vertices or patches of vertices asin previous stages of the graphics pipeline. If the tessellation isdisabled the geometry shader 819 receives input from the vertex shader807. The geometry shader 819 is programmable by a geometry shaderprogram to perform geometry tessellation if the tessellation units aredisabled.

Prior to rasterization, vertex data is processed by a clipper 829, whichis either a fixed function clipper or a programmable clipper havingclipping and geometry shader functions. In one embodiment, a rasterizer873 in the render output pipeline 870 dispatches pixel shaders toconvert the geometric objects into their per pixel representations. Inone embodiment, pixel shader logic is included in the thread executionlogic 850.

The graphics engine has an interconnect bus, interconnect fabric, orsome other interconnect mechanism that allows data and message passingamongst the major components of the graphics engine. In one embodimentthe execution units 852A, 852B and associated cache(s) 851, texture andmedia sampler 854, and texture/sampler cache 858 interconnect via a dataport 856 to perform memory access and communicate with render outputpipeline components of the graphics engine. In one embodiment, thesampler 854, caches 851, 858 and execution units 852A, 852B each haveseparate memory access paths.

In one embodiment, the render output pipeline 870 contains a rasterizerand depth test component 873 that converts vertex-based objects intotheir associated pixel-based representation. In one embodiment, therasterizer logic includes a windower/masker unit to perform fixedfunction triangle and line rasterization. An associated render and depthbuffer caches 878, 879 are also available in one embodiment. A pixeloperations component 877 performs pixel-based operations on the data,though in some instances, pixel operations associated with 2D operations(e.g. bit block image transfers with blending) are performed by the 2Dengine 841, or substituted at display time by the display controller 843using overlay display planes. In one embodiment a shared L3 cache 875 isavailable to all graphics components, allowing the sharing of datawithout the use of main system memory.

The graphics processor media pipeline 830 includes a media engine 337and a video front end 834. In one embodiment, the video front end 834receives pipeline commands from the command streamer 803. However, inone embodiment the media pipeline 830 includes a separate commandstreamer. The video front-end 834 processes media commands beforesending the command to the media engine 837. In one embodiment, themedia engine includes thread spawning functionality to spawn threads fordispatch to the thread execution logic 850 via the thread dispatcher831.

In one embodiment, the graphics engine includes a display engine 840. Inone embodiment, the display engine 840 is external to the graphicsprocessor and couples with the graphics processor via the ringinterconnect 802, or some other interconnect bus or fabric. The displayengine 840 includes a 2D engine 841 and a display controller 843. Thedisplay engine 840 contains special purpose logic capable of operatingindependently of the 3D pipeline. The display controller 843 coupleswith a display device (not shown), which may be a system integrateddisplay device, as in a laptop computer, or an external display deviceattached via an display device connector.

The graphics pipeline 820 and media pipeline 830 are configurable toperform operations based on multiple graphics and media programminginterfaces and are not specific to any one application programminginterface (API). In one embodiment, driver software for the graphicsprocessor translates API calls that are specific to a particulargraphics or media library into commands that can be processed by thegraphics processor. In various embodiments, support is provided for theOpen Graphics Library (OpenGL) and Open Computing Language (OpenCL)supported by the Khronos Group, the Direct3D library from the MicrosoftCorporation, or, in one embodiment, both OpenGL and D3D. Support mayalso be provided for the Open Source Computer Vision Library (OpenCV). Afuture API with a compatible 3D pipeline would also be supported if amapping can be made from the pipeline of the future API to the pipelineof the graphics processor.

Graphics Pipeline Programming—FIG. 9A-B

FIG. 9A is a block diagram illustrating a graphics processor commandformat according to an embodiment and FIG. 9B is a block diagramillustrating a graphics processor command sequence according to anembodiment. The solid lined boxes in FIG. 9A illustrate the componentsthat are generally included in a graphics command while the dashed linesinclude components that are optional or that are only included in asub-set of the graphics commands. The exemplary graphics processorcommand format 900 of FIG. 9A includes data fields to identify a targetclient 902 of the command, a command operation code (opcode) 904, andthe relevant data 906 for the command. A sub-opcode 905 and a commandsize 908 are also included in some commands.

The client 902 specifies the client unit of the graphics device thatprocesses the command data. In one embodiment, a graphics processorcommand parser examines the client field of each command to conditionthe further processing of the command and route the command data to theappropriate client unit. In one embodiment, the graphics processorclient units include a memory interface unit, a render unit, a 2D unit,a 3D unit, and a media unit. Each client unit has a correspondingprocessing pipeline that processes the commands. Once the command isreceived by the client unit, the client unit reads the opcode 904 and,if present, sub-opcode 905 to determine the operation to perform. Theclient unit performs the command using information in the data 906 fieldof the command. For some commands an explicit command size 908 isexpected to specify the size of the command. In one embodiment, thecommand parser automatically determines the size of at least some of thecommands based on the command opcode. In one embodiment commands arealigned via multiples of a double word.

The flow chart in FIG. 9B shows a sample command sequence 910. In oneembodiment, software or firmware of a data processing system thatfeatures an embodiment of the graphics processor uses a version of thecommand sequence shown to set up, execute, and terminate a set ofgraphics operations. A sample command sequence is shown and describedfor exemplary purposes, however embodiments are not limited to thesecommands or to this command sequence. Moreover, the commands may beissued as batch of commands in a command sequence, such that thegraphics processor will process the sequence of commands in an at leastpartially concurrent manner.

The sample command sequence 910 may begin with a pipeline flush command912 to cause any active graphics pipeline to complete the currentlypending commands for the pipeline. In one embodiment, the 3D pipeline922 and the media pipeline 924 do not operate concurrently. The pipelineflush is performed to cause the active graphics pipeline to complete anypending commands. In response to a pipeline flush, the command parserfor the graphics processor will pause command processing until theactive drawing engines complete pending operations and the relevant readcaches are invalidated. Optionally, any data in the render cache that ismarked ‘dirty’ can be flushed to memory. A pipeline flush command 912can be used for pipeline synchronization or before placing the graphicsprocessor into a low power state.

A pipeline select command 913 is used when a command sequence requiresthe graphics processor to explicitly switch between pipelines. Apipeline select command 913 is required only once within an executioncontext before issuing pipeline commands unless the context is to issuecommands for both pipelines. In one embodiment, a pipeline flush commandis 912 is required immediately before a pipeline switch via the pipelineselect command 913.

A pipeline control command 914 configures a graphics pipeline foroperation and is used to program the 3D pipeline 922 and the mediapipeline 924. The pipeline control command 914 configures the pipelinestate for the active pipeline. In one embodiment, the pipeline controlcommand 914 is used for pipeline synchronization and to clear data fromone or more cache memories within the active pipeline before processinga batch of commands.

Return buffer state commands 916 are used to configure a set of returnbuffers for the respective pipelines to write data. Some pipelineoperations require the allocation, selection, or configuration of one ormore return buffers into which the operations write intermediate dataduring processing. The graphics processor also uses one or more returnbuffers to store output data and to perform cross thread communication.The return buffer state 916 includes selecting the size and number ofreturn buffers to use for a set of pipeline operations.

The remaining commands in the command sequence differ based on theactive pipeline for operations. Based on a pipeline determination 920,the command sequence is tailored to the 3D pipeline 922 beginning withthe 3D pipeline state 930, or the media pipeline 924 beginning at themedia pipeline state 940.

The commands for the 3D pipeline state 930 include 3D state settingcommands for vertex buffer state, vertex element state, constant colorstate, depth buffer state, and other state variables that are to beconfigured before 3D primitive commands are processed. The values ofthese commands are determined at least in part based the particular 3DAPI in use. 3D pipeline state 930 commands are also able to selectivelydisable or bypass certain pipeline elements if those elements will notbe used.

The 3D primitive 932 command is used to submit 3D primitives to beprocessed by the 3D pipeline. Commands and associated parameters thatare passed to the graphics processor via the 3D primitive 932 commandare forwarded to the vertex fetch function in the graphics pipeline. Thevertex fetch function uses the 3D primitive 932 command data to generatevertex data structures. The vertex data structures are stored in one ormore return buffers. The 3D primitive 932 command is used to performvertex operations on 3D primitives via vertex shaders. To process vertexshaders, the 3D pipeline 922 dispatches shader execution threads tographics processor execution units.

The 3D pipeline 922 is triggered via an execute 934 command or event. Inone embodiment a register write triggers command execution. In oneembodiment execution is triggered via a ‘go’ or ‘kick’ command in thecommand sequence. In one embodiment command execution is triggered usinga pipeline synchronization command to flush the command sequence throughthe graphics pipeline. The 3D pipeline will perform geometry processingfor the 3D primitives. Once operations are complete, the resultinggeometric objects are rasterized and the pixel engine colors theresulting pixels. Additional commands to control pixel shading and pixelback end operations may also be included for those operations.

The sample command sequence 910 follows the media pipeline 924 path whenperforming media operations. In general, the specific use and manner ofprogramming for the media pipeline 924 depends on the media or computeoperations to be performed. Specific media decode operations may beoffloaded to the media pipeline during media decode. The media pipelinecan also be bypassed and media decode can be performed in whole or inpart using resources provided by one or more general purpose processingcores. In one embodiment, the media pipeline also includes elements forgeneral-purpose graphics processor unit (GPGPU) operations, where thegraphics processor is used to perform SIMD vector operations usingcomputational shader programs that are not explicitly related to therendering of graphics primitives.

The media pipeline 924 is configured in a similar manner as the 3Dpipeline 922. A set of media pipeline state commands 940 are dispatchedor placed into in a command queue before the media object commands 942.The media pipeline state commands 940 include data to configure themedia pipeline elements that will be used to process the media objects.This includes data to configure the video decode and video encode logicwithin the media pipeline, such as encode or decode format. The mediapipeline state commands 940 also support the use one or more pointers to“indirect” state elements that contain a batch of state settings.

Media object commands 942 supply pointers to media objects forprocessing by the media pipeline. The media objects include memorybuffers containing video data to be processed. In one embodiment, allmedia pipeline state must be valid before issuing a media object command942. Once the pipeline state is configured and media object commands 942are queued, the media pipeline 924 is triggered via an execute 934command or an equivalent execute event (e.g., register write). Outputfrom the media pipeline 924 may then be post processed by operationsprovided by the 3D pipeline 922 or the media pipeline 924. In oneembodiment, GPGPU operations are configured and executed in a similarmanner as media operations.

Graphics Software Architecture—FIG. 10

FIG. 10 illustrates exemplary graphics software architecture for a dataprocessing system according to an embodiment. The software architectureincludes a 3D graphics application 1010, an operating system 1020, andat least one processor 1030. The processor 1030 includes a graphicsprocessor 1032 and one or more general-purpose processor core(s) 1034.The graphics application 1010 and operating system 1020 each execute inthe system memory 1050 of the data processing system.

In one embodiment, the 3D graphics application 1010 contains one or moreshader programs including shader instructions 1012. The shader languageinstructions may be in a high-level shader language, such as the HighLevel Shader Language (HLSL) or the OpenGL Shader Language (GLSL). Theapplication also includes executable instructions 1014 in a machinelanguage suitable for execution by the general-purpose processor core1034. The application also includes graphics objects 1016 defined byvertex data.

The operating system 1020 may be a WINDOWS™ operating system availablefrom the Microsoft Corporation of Redmond, Wash., a proprietary UNIXoperating system, or an open source UNIX-like operating system using avariant of the Linux kernel. The operating system 1020 can support agraphics API 1022 such as the Direct3D API or the OpenGL API. When theDirect3D API is in use, the operating system 1020 uses a front-endshader compiler 1024 to compile any shader instructions 1012 in HLSLinto a lower-level shader language. The compilation may be ajust-in-time compilation or the application can perform sharepre-compilation. In one embodiment, high-level shaders are compiled intolow-level shaders during the compilation of the 3D graphics application1010.

The user mode graphics driver 1026 may contain a back-end shadercompiler 1027 to convert the shader instructions 1012 into a hardwarespecific representation. When the OpenGL API is in use, shaderinstructions 1012 in the GLSL high-level language are passed to a usermode graphics driver 1026 for compilation. The user mode graphics driveruses operating system kernel mode functions 1028 to communicate with akernel mode graphics driver 1029. The kernel mode graphics driver 1029communicates with the graphics processor 1032 to dispatch commands andinstructions.

To the extent various operations or functions are described herein, theycan be described or defined as hardware circuitry, software code,instructions, configuration, and/or data. The content can be embodied inhardware logic, or as directly executable software (“object” or“executable” form), source code, high level shader code designed forexecution on a graphics engine, or low level assembly language code inan instruction set for a specific processor or graphics core. Thesoftware content of the embodiments described herein can be provided viaan article of manufacture with the content stored thereon, or via amethod of operating a communication interface to send data via thecommunication interface.

A non-transitory machine readable storage medium can cause a machine toperform the functions or operations described, and includes anymechanism that stores information in a form accessible by a machine(e.g., computing device, electronic system, etc.), such asrecordable/non-recordable media (e.g., read only memory (ROM), randomaccess memory (RAM), magnetic disk storage media, optical storage media,flash memory devices, etc.). A communication interface includes anymechanism that interfaces to any of a hardwired, wireless, optical,etc., medium to communicate to another device, such as a memory businterface, a processor bus interface, an Internet connection, a diskcontroller, etc. The communication interface is configured by providingconfiguration parameters or sending signals to prepare the communicationinterface to provide a data signal describing the software content. Thecommunication interface can be accessed via one or more commands orsignals sent to the communication interface.

Data Distribution Fabric—FIG. 11-14

A hybrid data distribution fabric may be used as interconnecting logicfor an embodiment of a graphics processor featuring scalable GPUs. Inone embodiment, the hybrid fabric includes one or more physical datachannels operating over a shared bus, with one or more programmablevirtual channels on each physical channel. The virtual channels may bearbitrated independently, with channel access negotiated separately pervirtual channel. Traffic over the virtual channels may be classifiedinto one or more traffic classes. In one embodiment, a prioritizationsystem allows virtual channels and traffic classes to be assigned arelative priority for arbitration. In one embodiment, traffic balancingalgorithms operate to maintain substantially equal bandwidth andthroughput to each node coupled to the fabric. In one embodiment, thehybrid fabric data distribution logic operates at a higher clock ratethan the nodes couples to the fabric, allowing a reduced bus width whilemaintaining bus throughput. In one embodiment, each shared bus isseparately clock gated when idle and sends an early indication ofupcoming activity to trigger a bus wake event.

FIG. 11 is a block diagram of an embodiment of a graphics core fabricassembly 1100 including a graphics core 1102, graphics core cache 1104,and hybrid fabric connector 1106. The hybrid fabric connector 1106couples the graphics core fabric assembly 1100 to a fabric bus 1108. Anembodiment of the hybrid data distribution fabric assembly 1100 isavailable for multiple levels of abstraction within the graphicsprocessor. The graphics core 1102 includes any of the graphics executionlogic described herein, such as a the scalable execution unit array 414of FIG. 4, graphics cores 580A of FIG. 5, or an execution unit 608A ofFIG. 6. Graphics core cache 1104 includes local graphics core cachememory, which stores incoming data from the fabric connector 1106. Thegraphics core cache 1104 can also store outgoing data beforetransmission by the data distribution fabric connector 1106.

The fabric connector 1106 is a fabric node that can receive, buffer,transmit, and re-transmit packets of data along the hybrid fabric 1108.The hybrid fabric connector 1106, in one embodiment, receives a packeton one channel of the hybrid fabric and switches the packet byre-transmitting the packet over a different channel. An embodiment ofthe hybrid fabric connector 1106 couples with the graphics core cache1104. The connector 1106 writes data destined for the graphics core 1102into the graphics core cache 1104, and reads data from the graphics corecache 1104 for transmission to shared memory, or to a different graphicscore. Each graphics core has a core identifier and a hash identifierthat are used to address data packets on the hybrid fabric and toperform traffic load balancing across the fabric nodes.

The hybrid fabric bus 1108 may include a single bus line or multiple buslines. In one embodiment, the hybrid fabric bus 1108 includes multipleprogrammable data channels over which packet-based data messages aretransmitted for each graphics core 1102. The multiple channels of thehybrid fabric bus 1108 are shared between the multiple graphics coresand support multiple traffic classes of data. The number of channels isconfigurable based on the number of graphics cores, the graphics coreworkload, and the utilization and capacity of the memory in the graphicsprocessing system (e.g., local/shared cache, system memory, etc.).

FIGS. 12A-B illustrate multiple exemplary graphics core topologies. FIG.12A shows a tree topology in which nine graphics cores are coupled viaan embodiment of the hybrid fabric. FIG. 12B shows a mesh topology inwhich sixteen graphics cores are coupled via an embodiment of the hybridfabric. The hybrid fabric is configurable for each of the possiblegraphics core topologies. The graphics cores may be arranged in astacked 3D integrated circuit including multiple graphics cores inmultiple vertical layers. The stacked integrated circuit may include adie-on-die integrated circuit, a wafer-on-wafer integrated circuit,and/or one or more combinations of wafer-on-die or die-on-wafercircuits. However, other 3D circuit manufacturing methods may also beused.

FIG. 12A shows nine graphics cores are coupled in a tree topology. Afirst layer 1200 includes three graphics cores, where a first graphicscore 1202, couples with a second graphics core 1204 via a third graphicscore 1206. The third graphics core 1206 couples with a sixth graphiccore 1216 in a second layer 1210 via one or more through-silicon-vias(“TSV”s). Additionally, the sixth graphics core 1216 couples a fourthgraphics core 1212 with a fifth graphics core 1214. The sixth graphicscore 1216 additionally couples with a ninth graphics core 1226 in athird layer 1220, which includes a seventh graphics core 1222 and aneighth graphics core 1224. The graphics cores, via the hybrid fabric,couple and communicate with shared resources 1230 including sharedmemory and other common resources shared by the graphics cores, suchshared pixel back end hardware. The hybrid fabric may be configured toprovide additional bandwidth or throughput to high-traffic hybrid fabricconnectors, or provide other load balancing or traffic managementtechniques to maintain substantially equal bandwidth for data flowingto, from, and through each graphics core.

In the exemplary block diagram of FIG. 12B, sixteen graphics cores areassembled in a mesh topology. In one possible configuration, fourlayers, each having four graphics cores, are stacked. A first layer 1240includes four graphics cores, where each graphics core couples with acounterpart graphics core in a second layer 1250. Next, each graphicscore in the second layer 1250 couples with a counterpart graphics corein the third layer 1260. Next, each graphics core in the third layer1260 couples with a counterpart graphics core in a fourth layer 1270.Finally, each graphics core in the fourth layer 1270 couples with sharedresources 1280, including shared memory. The number of layers, and thenumber of cores per layer is exemplary and embodiments are not solimited, and multiple topologies are supported. The hybrid fabric may beconfigured to enable communication between multiple graphics coresarranged in differing topologies based on die-size, bandwidth andthroughput requirements.

FIG. 13 is a block diagram of an embodiment of a stacked 3D integratedcircuit including five vertically stacked graphic cores. The fabricchannels illustrated may be separate buses or may be wired over a sharedbus. Each graphics core may send or receive data on any channel. Datapackets travelling on the hybrid fabric may pass through the fabricconnectors of multiple cores before reaching the target. While a coremay conduct cross-core communication on a single channel, a packet maybe switched from channel to channel when transiting a core, or a fabricconnector coupled to the core. A channel arbitration algorithm may beemployed to balance traffic on each channel to maintain equalcommunications bandwidth for each core. While graphics cores areillustrated, a fabric connector coupled to the graphics core may performat least some of the described functionality.

An example arbitration algorithm is the ‘stack optimization’ algorithmused for memory bound traffic. The graphics processor cores 1302-1310shown in FIG. 13 each couples with a respective hybrid fabric connector(e.g., hybrid fabric connector 1106 of FIG. 11). The hybrid fabricconnectors couple the interconnected cores with a region of sharedmemory 1330. Table 1 below illustrates the results of an exemplarychannel arbitration algorithm to balance memory-bound traffic betweenfive graphics cores and shared memory.

TABLE 1 Stack Optimization Algorithm Fabric Logic in Respective CoresChannel 0 Channel 1 Channel 2 Channel 3 Channel 4 Core 0 Core 0 TrafficCore 1 Traffic Core 2 Traffic Core 3 Traffic Core 4 Traffic ChannelAssignment Core 1 Core 1 Traffic Core 2 Traffic Core 3 Traffic Core 4Traffic Core 0 Traffic Channel Assignment Core 2 Core 2 Traffic Core 3Traffic Core 4 Traffic Core 0 Traffic Core 1 Traffic Channel AssignmentCore 3 Core 3 Traffic Core 4 Traffic Core 0 Traffic Core 1 Traffic Core2 Traffic Channel Assignment Core 4 Core 4 Traffic Core 0 Traffic Core 1Traffic Core 2 Traffic Core 3 Traffic Channel Assignment

As shown in the Channel 0 column of Table 1, each core is configured tooriginate memory bound data on channel 0, while switching pass-throughtraffic from other cores to other channels. For example, a memory bounddata packet 1312 is transmitted from graphics core zero 1302 on channel0. Core one 1304 switches the packet 1314 to channel four because thestack optimization algorithm specifies that memory bound traffic fromcore zero 1302 is to pass through on channel four. Thus, core two 1306switches the packet 1316 to channel three. Core three 1308 switches thepacket 1318 to channel two. Core four 1310 switches the packet 1320 tochannel one. While FIG. 13 and Table 1 illustrate an exemplary algorithmfor an exemplary type of traffic on the hybrid fabric. Other algorithmsmay be used for other types of traffic. In one embodiment, differingtypes of traffic are grouped into differing traffic classes to betterfacilitate traffic management.

FIG. 14 is an illustration of multiple traffic classes carried overvirtual channels, according to an embodiment. A first fabric connector1402 and second fabric connector 1404 facilitate communication over afabric channel 1406 having up to ‘M’ virtual channels 1406A-M. Thevirtual channels enable the transfer of variable length information overa fixed set of physical channels. The virtual channels may be permanentvirtual channels, or the virtual channels may be dynamically enabled ordisabled based on the system configuration. Using permanent virtualchannels allows fixed channel IDs, which minimizes the overhead ofvirtual channel management. Dynamically configuring channels increasesdesign flexibility at the expense of additional channel managementoverhead.

Each virtual channel may be assigned multiple traffic classes. A trafficclass (e.g., 1408) is a division of traffic that is related forarbitration. Each virtual channel may carry up to ‘N’ traffic classes.Each class of traffic is assigned to a specific virtual channel throughprogramming (fuses, configuration registers etc.). Up to ‘L’ classes oftraffic types may be assigned to a given virtual channel.

TABLE 2 Traffic Class Assignment # Traffic Class Virtual Channel 1 Class1 1 2 Class 2 0 3 Class 3 M 4 Class 4 1 5 Class 5 0 . . . N Class N 2

Table 2 above shows an exemplary traffic class to virtual channelassignment as illustrated in FIG. 14. The hybrid fabric classifies eachunit of incoming traffic and may include logic to ensure that theincoming unit travels within its assigned virtual channel. In oneembodiment, data transmission over the channels occurs infirst-in-first-out (FIFO) order, and channel arbitration occurs based onvirtual channels. Traffic within a virtual channel may block thetransmission of additional traffic on the same virtual channel. However,a given virtual channel will not block a different virtual channel.Accordingly, traffic on different virtual channels is arbitratedindependently.

In one embodiment, coherency is maintained during data transmission forindividual threads operating on a graphics core at both the graphicscore cache and at the hybrid fabric connector node for the graphicscore. The hybrid fabric nodes route traffic originating from a singlethread within the same traffic class, and the traffic classes areassigned to a specific virtual channel. Data within a single trafficclass on a single virtual channel is transmitted in FIFO order. Thus,data from a single thread is strictly ordered when transmitted via thehybrid fabric, and per-thread coherency is maintained, to avoidread-after-write or write-after-read data hazards. In one embodiment,thread group coherency is maintained via a global synchronizationmechanism with shared memory.

TABLE 3 Traffic Class Prioritization Traffic # Class Priority 1 Class 12 2 Class 2 1 3 Class 3 4 4 Class 4 2 5 Class 5 1 . . . N Class N 3

Table 3 above shows an exemplary traffic class prioritization. Apriority algorithm may be programmed to determine the priority to assignto each of the traffic classes. The programmable traffic classpriorities allow the traffic classes to be used as an arbitrary trafficgrouping mechanism, where traffic may be grouped within a class merelyto maintain coherency, or specific traffic can be assigned a highpriority and dedicated to high priority data. For example, class 1 andclass 4, each assigned to virtual channel one 1406B, may be assigned apriority of 2. Class 2 and class 5, each assigned to virtual channelzero 1406A, may be assigned a priority of 1. A traffic class ‘N’ may beassigned to virtual channel two 1406C with a priority of 3. Traffic inclass 2 may be latency sensitive data that should be transmitted as soonas possible or should not be blocked by other traffic classes, whiletraffic in class 1 may be moderately latency sensitive traffic from asingle thread that is grouped to maintain coherency.

A traffic class may be assigned a priority relative to all trafficclasses or relative to the priority of traffic classes on the samevirtual channel. In one embodiment, the priority scheme is designed byassigning weights to the traffic classes, where a higher weightindicates a higher priority. A fair prioritization algorithm may beemployed, where each participant is guaranteed a minimum amount ofbandwidth to prevent starvation. In one embodiment, an absolute priorityalgorithm is used under certain circumstances, where higher prioritytraffic always blocks lower priority.

Where absolute priority is in use, additional algorithms are in place toprevent a communication deadlock. The use of virtual channels andtraffic classes in combination reduces the likelihood of a deadlock, asa single traffic class having absolute priority on a given virtualchannel does not block traffic on a different virtual channel. In oneembodiment, if a starvation condition or a potential deadlock isdetected on one virtual channel, blocked traffic classes may bere-assigned to a different virtual channel.

TABLE 4 Virtual Channel Prioritization # Virtual Channel Priority 1 1 22 2 1 3 3 3 . . . M M 4

Table 4 below shows an exemplary virtual channel prioritization. As withtraffic classes, each virtual channel may also receive a priority andchannel arbitration can factor the relative priorities of the virtualchannels. For example, data traffic on virtual channel 2 may have ahigher relative priority than data on other virtual channels. A weightedpriority system may be employed with virtual channel prioritization,where a higher weight indicates a higher priority. A fair prioritysystem or an absolute priority system may be used.

FIG. 15 is a flow diagram of a data transmission sequence, according toan embodiment. A source node, such as a hybrid fabric connector coupledto a graphics processor, determines channel access status for a channelbefore transmitting a message packet over a channel on the hybridfabric, as shown at block 1502. The message can be classified into oneof multiple possible traffic classifications, each classification havinga relative priority on the channel. Channel access can be determined viaany suitable channel access protocol, such as a time division multipleaccess protocol, or a carrier sense multiple access protocol.

Having determined that a first channel is available, the source node cantransmit the message from the source node towards a target node, asshown at block 1504. The message can be received by a first node on theshared bus of the hybrid fabric, as shown at block 1506. The first nodemay be coupled to one of multiple graphics processors coupled by thehybrid fabric. Based on several factors, such as the source node, thetarget node, the traffic class, and the channel in which the message isreceived, the first node may switch the message from the first node tothe second node on the shared bus, as shown at block 1508. The firstnode may switch the message as part of a traffic balancing protocol,such as the stack optimization algorithm of Table 1, or as part of adirectional routing protocol, depending on the graphics core topologyserved by the hybrid fabric. In one embodiment, channel access isdetermined based on multiple virtual channels carried across a sharedbus, where channel access for each virtual channel is arbitratedseparately from other virtual channels.

In one embodiment the hybrid fabric interconnect logic operates at ahigher clock frequency than the nodes connected by the interconnectlogic. A single message between nodes may be divided into a number ofseparate messages based on the frequency ratio between the fabricinterconnect and the nodes. A fabric node may transmit a message duringeach of the node's clock cycles, and the message is divided intomultiple messages to be sent between clock cycles. The division of themessage is transparent to the fabric node, allowing a reduction in thewidth of the physical layer of the interconnecting logic whilemaintaining performance.

In one embodiment, the interconnect logic of the hybrid fabric is powermanaged and clock gated. A distributed approach may be used for clockgating, where each bus line uses a local gated clock that is disabledwhen the bus is idle. Each bus issues an early indication of incomingactivity, which enables the clock when a message is to be received alongthe bus, or a virtual channel associated with the bus. Accordingly,power is dissipated only on active buses. While idle, a bus consumesonly static power, and is otherwise in a low power state.

The terms “first,” “second,” “third,” “fourth,” and the like in thedescription and in the claims, if any, are used for distinguishingbetween similar elements and not necessarily for describing a particularsequential or chronological order. It is to be understood that the termsso used are interchangeable under appropriate circumstances such thatthe embodiments described herein are, for example, capable of operationin sequences other than those illustrated or otherwise described herein.

As used herein, references to one or more “embodiments” are to beunderstood as describing a particular feature, structure, orcharacteristic included in at least one implementation. Thus, phrasessuch as “in one embodiment” or “in an alternate embodiment” appearingherein, each describe various embodiments and implementation, and do notnecessarily all refer to the same embodiment. However, they are also notnecessarily mutually exclusive.

In one embodiment, a processor comprises one or more graphics cores andinterconnecting logic having at least one data channel to interconnectthe one or more graphics processor cores. The at least one data channelmay be carried over a shared bus. The interconnect logic couples theinterconnected cores with a shared resource. The interconnect logicenables data distribution between the interconnected cores and theshares resource over one or more virtual channels carried over the atleast one data channel. The virtual channels may include a programmabletraffic classification system having multiple classifications oftraffic.

The multiple classifications of traffic may have priorities assigned toeach classification. The priorities may be arbitrated relative to othertraffic classifications on the same virtual channel. In one embodimentthe one or more graphics processor cores comprise a 3D integratedcircuit stack including multiple graphics processor cores. In oneembodiment, the multiple graphics processor cores are coupled viamultiple shared buses, where each bus is separately clock gated duringidle periods.

In one embodiment, a system comprises a processor including a pluralityof cores, where at least one core includes an instruction set forprocessing graphics instructions. The at least one graphics processingcore couples with a shared resource on the processor via interconnectlogic having at least one clock gated physical data channel and one ormore virtual channels, each virtual channel to carry data havingmultiple traffic classifications. The multiple traffic classificationsmay be programmable, and each of the multiple traffic classificationsmay be assigned to a virtual channel. The system may also include memorycoupled to the processor.

Data representing a design to perform an embodiment described herein mayrepresent the design in a number of manners. First, as is useful insimulations, the hardware may be represented using a hardwaredescription language or another functional description language.Additionally, a circuit level model with logic and/or transistor gatesmay be produced at some stages of the design process. Furthermore, mostdesigns, at some stage, reach a level of data representing the physicalplacement of various devices in the hardware model. In the case whereconventional semiconductor fabrication techniques are used, the datarepresenting the hardware model may be the data specifying the presenceor absence of various features on different mask layers for masks usedto produce the integrated circuit. In any representation of the design,the design data may be stored in a form of a machine-readable medium.

In one embodiment, a machine-readable medium stores data, which ifperformed by at least one machine, causes the at least one machine tofabricate at least one integrated circuit to perform a method comprisingdetermining a channel access status on a multiple node shared bus for amessage from a source node to a target node, wherein at least one of themultiple nodes couples with a graphics processor core and at least oneof the nodes couples with a shared resource, transmitting a message fromthe message source to a message target over a first data channel, wherethe message includes a first traffic classification having a firstpriority, receiving the message at a first data bus connector coupledwith a graphics processor core, and based on at least the source nodeand the target node, switching the message from a first data channel toa second data channel. The at least one integrated circuit fabricatedmay be a 3D integrated circuit stack including multiple graphicsprocessor cores.

In one embodiment, determining channel access comprises determining,using a channel access protocol, if a message can be transmitted over athird data channel, and after determining that transmission over thethird data channel is blocked, transmitting a message over the firstdata channel. Channel access may be determined by a time divisionmultiple access protocol or a carrier sense multiple access protocol.

Various components described can be a means for performing theoperations or functions described. Each component described hereinincludes software, hardware, or a combination of these. The componentscan be implemented as software modules, hardware modules,special-purpose hardware (e.g., application specific hardware,application specific integrated circuits (ASICs), digital signalprocessors (DSPs), etc.), embedded controllers, hardwired circuitry,etc. Besides what is described herein, various modifications can be madeto the disclosed embodiments and implementations without departing fromtheir scope. Therefore, the illustrations and examples herein should beconstrued in an illustrative, and not a restrictive sense. The scope andspirit of the invention should be measured solely by reference to theclaims that follow.

What is claimed is:
 1. A processor comprising: a general purposeprocessor core; a three-dimensional (3D) integrated circuit stackincluding multiple graphics processor cores, the 3D integrated circuitstack coupled to the general purpose processor core; and interconnectlogic having at least one data channel, to interconnect the graphicsprocessor cores of the 3D integrated circuit stack and couple thegraphics processor cores with a shared resource, the interconnect logicfurther to enable data distribution between the graphics processor coresand the shared resource over a virtual channel including multipleprogrammatically pre-assigned traffic classifications.
 2. The processorof claim 1, wherein the at least one data channel is a shared bus. 3.The processor of claim 1, wherein the interconnect logic includesmultiple data channels.
 4. The processor of claim 3, wherein each of themultiple data channels is a separately clock gated bus, and wherein eachbus is to use early indications to signal incoming activity.
 5. Theprocessor of claim 1, wherein the shared resource is a shared memoryresource.
 6. The processor of claim 5 wherein the shared memory resourceis a shared cache.
 7. The processor of claim 1, wherein the interconnectlogic is to enable the data distribution over multiple virtual channels,the multiple virtual channels including the virtual channel and one ormore additional channels.
 8. The processor of claim 7, wherein themultiple virtual channels are to be arbitrated based on a programmablepriority system.
 9. The processor of claim 8, wherein each of themultiple virtual channels is to be assigned multiple trafficclassifications.
 10. The processor of claim 9, wherein each of themultiple traffic classifications includes a programmable priority. 11.The processor of claim 10, wherein the programmable priority is relativeto traffic classifications within a same virtual channel of the multiplevirtual channels.
 12. The processor of claim 1, wherein the interconnectlogic operates at a higher frequency than the graphics processor cores.13. The processor of claim 1, additionally including a set ofinterconnect nodes to couple the graphics processor cores with theinterconnect logic, wherein the interconnect logic includes multipledata channels and the set of interconnect nodes is configured to switchdata between the multiple data channels when transiting one of thegraphics processor cores.
 14. A system comprising: a processor includinga three-dimensional (3D) circuit stack including a plurality of cores,at least one of the plurality of cores including an instruction set forprocessing graphics instructions, the at least one core to be coupledwith a shared resource on the processor via interconnect logic having atleast one clock gated physical data channel and a set of virtualchannels including one or more virtual channels, the one or more virtualchannels having multiple programmatically pre-assigned trafficclassifications; and memory coupled to the at least one core and theinterconnect logic, the memory to store data for the at least one corebefore transmission via the interconnect logic.
 15. The system as inclaim 14 wherein the shared resource on the processor is a shared memoryresource.
 16. The system as in claim 15, wherein the shared memoryresource includes a shared cache memory.
 17. The system of claim 14,wherein the set of virtual channels includes multiple virtual channels,wherein the multiple virtual channels in the set of virtual channels areto be arbitrated based on a programmable priority system.
 18. The systemof claim 17, wherein each of the multiple programmable trafficclassifications is prioritized relative to other traffic classesassigned to the same virtual channel of the multiple virtual channels.19. The system of claim 14, wherein the system is a system on a chipintegrated circuit.
 20. A non-transitory machine-readable medium havingstored thereon data, which if performed by at least one machine, causesthe machine to fabricate a system on a chip integrated circuit includinga three-dimensional (3D) circuit stack of multiple graphics processorcores to perform a method comprising: determining a channel accessstatus on a multiple node shared bus for a message from a source node toa target node, wherein at least one node of the multiple node shared buscouples with a graphics processor core of integrated circuit and atleast one node of the multiple node shared bus couples with a sharedresource on the integrated circuit; transmitting a message from thesource node to the target node over a first data channel, wherein themessage is associated with a first traffic classification having a firstpriority; receiving the message at a first data bus connector coupledwith the graphics processor core; and based on at least the source nodeand the target node, switching the message from the first data channelto a second data channel.
 21. The non-transitory machine-readable mediumof claim 20, additionally including determining that the message isassociated with the first traffic classification and switching themessage from the first data channel to the second data channel based atleast on the first traffic classification.
 22. The non-transitorymachine-readable medium of claim 20, wherein determining the channelaccess status comprises: determining, using a channel access protocol,if a third data channel is available to transmit the message from thesource node to the target node; and after determining that transmissionover the third data channel is blocked, transmitting the message overthe first data channel.
 23. The non-transitory machine-readable mediumof claim 22, wherein the first, second, and third data channel arevirtual data channels.
 24. The non-transitory machine-readable medium ofclaim 22, wherein the channel access protocol is a time divisionmultiple access protocol.
 25. The non-transitory machine-readable mediumof claim 22, wherein the channel access protocol is a carrier sensemultiple access protocol.